Carrier transport properties of the Group-IV ferromagnetic semiconductor Ge1-xFex with and without boron doping

TL;DR

This study investigates the transport and magnetic properties of Ge1-xFex ferromagnetic semiconductors with boron doping, revealing that increased hole concentration does not influence magnetic behavior, contrasting with III-V semiconductors.

Contribution

It provides new insights into the transport and magnetic properties of Ge1-xFex films, especially regarding the effects of boron doping and the lack of correlation between hole concentration and ferromagnetism.

Findings

Hole concentration increased with boron doping.

No correlation between hole concentration and magnetic properties.

Negligible anomalous Hall effect in the films.

Abstract

We have investigated the transport and magnetic properties of group-IV ferromagnetic semiconductor Ge1-xFex films (x = 1.0 and 2.3 %) with and without boron doping grown by molecular beam epitaxy (MBE). In order to accurately measure the transport properties of 100-nm-thick Ge1-xFex films, (001)-oriented silicon-on-insulator (SOI) wafers with an ultra-thin Si body layer (~5 nm) were used as substrates. Owing to the low Fe content, the hole concentration and mobility in the Ge1-xFex films were exactly estimated by Hall measurements because the anomalous Hall effect in these films was found to be negligibly small. By boron doping, we increased the hole concentration in Ge1-xFex from ~1018 cm-3 to ~1020 cm-3 (x = 1.0%) and to ~1019 cm-3 (x = 2.3%), but no correlation was observed between the hole concentration and magnetic properties. This result presents a contrast to the hole-induced ferromagnetism in III-V ferromagnetic semiconductors.